Apparatus for blow molding plastic articles

ABSTRACT

An apparatus for blow molding articles by preinflating a tubular parison prior to final expansion within the blow mold. The apparatus includes a clamping assembly for sealing a leading end of the extruding parison, and a specially configured mandrel tip which is axially movable against a shoulder in the extrusion head to at least partially sever the parison situated therebetween after preinflation.

States atent [1s] 3,,3111:; Shaw et all. 1 1 Mn, 1, MW

[54] APPARATUS FOR BLOW MOLDENIG 3,327,350 6/1967 Limbach ..1s 5 avPLASTIC AR'HQLES 3,488,803 1/1970 Cote ..18/5 BA 3,425,090 2/1969 Naveet 311.... .....18/5 132 "Charles Shaw, Bloomfield; Robert 3,430,2903/1969 Kinslow ..18/5 BQ Strauss, West Hartford, both of Conn.

' FOREIGN PATENTS OR APPLICATIONS [73] Monsanto Company, St. Louis, Mo.

631,830 11962 It] ..l85BZ 221 Apr. 10, 1969 I a y I [21] PrimaryExaminer-H. A. Kilby, Jr.

Attorney-James C. Logomasini and Herbert B. Roberts Related US.Application Data [62] Division of Ser. No. 587,255, Oct. 17, 1966. [57]ABSTRACT An apparatus for blow molding articles by preinflating a tubu-[52] US. Cl ..425/297, 425/301, 425/387 lar parison prior to finalexpansion within the blow mold. The [51] Int. Cl ..B29dl 23/03 apparatusincludes a clamping assembly for sealing a leading [58] Field oi Search1 8/5 HQ, 5 B2, 5 BA, 5 BE end of the extruding parison, and a speciallyconfigured mandrel tip which is axially movable against a shoulder inthe ex- References Cited UNITED STATES PATENTS Schaich 13/; BQ X trusionhead to at least partially sever the parison situated therebetween afterpreinflation.

2 Claims, 9 Drawing Figures PATENTEBJANTSKSYZ 3,635,632

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INVENTOR. CHARLES H. SHAW ROBERT G STRAUSS BY W7 ATTORNEY 9 1 1 u ll!! oN .v I l fiA/ 0.2.0 fl M MPfi m V? Z W a w,

PATENTEUJANIZJISYZ 3,635,632

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Ill-3 INVENTOR. CHARLES H. SHAW ROBERT G. STRAUSS ATTORNEYATENYEUJAM8B72 3,685,632

SHEET 3 UF 4 FIG. 5

J WA m CHARLES H. SHAW ROBERT G. STRAUSS ATTORNEY INVENTOR.

PATENTEU W 8131;

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INVENTOR. CHARLES H. SHAW ROBERT G. STRAUSS FIG. 7

ATTORNEY APPARATUS FOR BLOW MOLDING PLASTIC ARTICLES This is a divisionof copending application Ser. No. 587,255, filed Oct. l7, 1966.

This invention relates to improvements in apparatus for forming plasticarticles, and more particularly to an improved apparatus for blowmolding plastic articles.

In blow molding articles, for example bottles, by expanding a heatedtube or parison of thermoplastic material against the walls of a hollowmold, chilling and setting of the plastic occurs almost instantaneouslyon contact of the plastic with the walls of the mold cavity. When thissetting of the plastic occurs, no further expansion is possible, so thatthe parts of the body of the bottle first contacting the mold walls aregenerally of greater wall thickness than those parts formed by latercontact with the walls. It has been particularly difficult in the past,therefore, to blow mold noncylindrical or irregularly shaped bottleswith a uniform wall thickness wherein certain sections of the parisonmust be expanded further than other portions which may have alreadycontacted the mold walls. Uneven wall thickness results in poor impactstrength causing the bottles to break or buckle in the thinner sectionswhen top loaded, e.g., when stacked.

The difficulty has been especially pronounced in blow molding the morerecently developed handleware bottles wherein a hand hole radiallyoffset from the axis of the bottle is provided by expanding the parisonaround cooperating protrusions extending from the walls of each moldhalf. These cooperating protrusions matingly contact when the mold isclosed and represent the mold configuration which yields the handhole inthe finished article. To produce such a bottle it has been necessary toposition the parison asymmetrically within the closed mold so that thepart of the parison which ultimately forms the body of the bottleadjacent the handhole is located quite close to the corresponding wallof the mold cavity, while that part which will form the opposite side islocated considerably further away from its confining cavity wall andmust be expanded over a greater distance. n expansion, nonuniform wallthickness results, with the amount of plastic material in the area ofthe hollow handle and adjacent wall being greater than that in thediametrically opposite wall due to the difference in the amount ofexpansion which each side of the parison has undergone. To overcome thisvariability, extremely large diameter parisons requiring minimumexpansion have been used, but this approach results in excessive wastein the tail pinch area, is uneconomical unnecessarily increases theweight of the plastic in the container, and requires larger extrusiontooling (i.e., mandrels, dies) to produce the larger diameter parison.

Accordingly it is the principle object of the present invention toprovide apparatus for producing hollow plastic articles havingnoncylindrical cross sections with improved wall thickness distribution.

It is a particular object of this invention to provide apparatus foreconomically forming hollow plastic articles having noncylindrical crosssections with improved wall thickness distribution while avoidingexcessive plastic consumption in formation of the article.

It is a further object of the present invention to provide apparatus forforming hollow articles of noncylindrical cross section by modifying theshape of a normally tubular blank from which the articles is formed, toa configuration more nearly conforming to that of the finished article.

It is a further object of this invention to provide apparatus forforming hollow plastic articles having noncylindrical cross sectionswherein the amount of tail pinch is reduced.

It is an additional object of this invention to provide ap' paratus forforming hollow plastic handle type bottles.

It is a further object of this invention to provide apparatus forforming hollow plastic articles which allows the use of smallerextrusion tooling.

It is a further object of this invention to provide an improvedapparatus for cutting, sealing and supporting an extruded parison.

It is a still further object of the present invention to provide meansto carry out the above objects.

Other objects of this invention will in part be obvious and will in partappear hereinafter.

These and other objects are accomplished by providing an apparatus forforming hollow plastic articles having neck and body portions, theapparatus involving extruding moldable plastic material from a supplysource downwardly through an outlet orifice to form a generally tubularlength of the material, clamping the tubular length below the outletorifice to form a seal across the tubular length, injecting gas into theportion of the length above the seal to partially expand said portion,enclosing the partially expanded shape within a partible mold havingadjacent neck and body forming cavities, and further expanding thepartially expanded shape to form the hollow article.

In describing the overall invention, reference will be made to preferredembodiments illustrated in the accompanying drawings, in which:

FIG. l is a partial, schematic, vertical, sectional view illustratingthe preferred apparatus embodiment at an early stage in the presentinventive process with the preinflation gas on;

FIG. 2 is a partial, schematic, vertical, sectional view illustratingthe parison cutting and sealing step of the process;

FllG. 3 is a schematic vertical sectional view illustrating the expandedparison and blowhead assembly;

FIG. Al is a plan view illustrating the complete parison cutting andsealing assembly;

FIG. 5 is a side, elevational view of an alternate embodiment of thepresent invention illustrating parison-gripping apparatus;

FIG. 6 is a plan view taken along the line 66 of FIG. 5;

FIG. 7 is a partial, schematic, vertical, sectional view illustrating amodified form of the present invention from that depicted in FIGS. 1 and2;

FIG. 8 is a partial, schematic, vertical, sectional view illus tratingthe cut parison of the modified form of the present invention depictedin FIG. 7; and

FIG. 9 is a partial, schematic, vertical, sectional view illustratingthe parison sealing step of the modified form of the invention depictedin FIG. 7.

With reference to the drawings wherein identical numerals refer toidentical parts, there is shown in FIG. 1 a generally vertical extrusionhead 12 having one side attached to an end of horizontal conduit 10,which in turn may have its other end connected to the discharge of aconventional worm extruder, not shown, Extrusion head 12 has acylindrical exterior wall 13, and a generally cylindrical verticallyextending reservoir 15 communicating with opening ill in horizontalconduit it). Cylindrical inner core or mandrel 22 is mounted withinreservoir 15 so as to define an annular cavity. At the lower end of theillustrated inner core 22, there is mounted an extrusion tip 23 whichprovides an inner surface of a parison defining outlet through which aheated and suitably homogenized organic plastic resin such as, forexample, polyethylene is extruded in generally tubular form. Extrusionring 26 is provided at the lower end of the extrusion head 12 havingcurved shoulder 27 which cooperates with generally convex downwardsurface 241 of extrusion tip 23 so as to define an annular outletorifice M in axial alignment with tip 23. inner core 22 is bored toprovide passageway 28 therein. Gas pressure supply conduit 36} has itsopposite ends connected with passageway 23 and with a suitablelow-pressure gas supply source (not shown). The communication may becontinually maintained or gas pressure supplied at timed intervals as bymeans of control valve 32 mounted in line 30 between passageway 2t andthe gas supply source.

Multisection mold lid having mold sections and Nb is provided to form acavity generally designated 20 in which to blow mold and shape anarticle. Extrusion head 112 is so disposed that mold it may be broughtinto registry therewith.

In the illustrated embodiments, mold sections llfia and Nb arepreferably mounted on a conventional rotary turret table not shown whichpreferably carries a plurality of equally spaced molds not shown,identical with mold 18. As is hereinafter described in greater detail,operation of mold 18 may be automatically controlled in timed sequencewith the operation of extrusion head 12 and other components of theapparatus by suitable timing mechanisms not shown.

Referring now to the parison cutting and sealing apparatus which is aspecial feature of the present invention as illustrated in FIG. 4, thereis provided a piston operated scissors like assembly 34. Piston 36 isconnected to rod 38 within housing 39. Toggle joint 41 comprises cutterpivot member 40 and sealer pivot member 42, and rod extension 46, allthree being pivotably mounted together on toggle pin 44, with rodextension 46 rigidly joined to rod 38.

Pivot member 40 has one end pivotably connected at 48 to cutter bladesupport member 50. Sealer pivot member 42 is a likewise pivotablyconnected at one end at 52 to sealer blade support member 54. Sealerblade 56 is joined, for example, by conventional bolting to sealer bladesupport member 54 at 58. Cutter blade 60 is likewise conventionallybolted at 62 to cutter blade support member 50. Adjustable cutter bladeeccentric bushing 64 is provided to permit varying the amount of travelof the cutter blade in relation to the sealer blade. That is, the amountof open space between blades 56 and 60 may be varied from that shown inFIG. by means of adjustable eccentric bushing 64. This adjustment isdesirable to compensate for the varying parison wall thicknesses anddiameters encountered. Sealer blade bushing 66 is mounted in sealerblade support member 54 and may also be an adjustable eccentric, thoughordinarily only one is required per assembly. Mounting of the adjustableeccentric may be either on the cutter or sealer blade assembly. Bushings64 and 66 also represent the pivot points about which the cutter andsealer support members rotate when piston 36 is activated. Thoughdesirable, the adjustable eccentric feature of the bushing may beeliminated and any means provided to permit pivoting support members 50and 54; a bearing or pivot pin for example may be utilized. Likewise thepivot means may be mounted in the blades and the support memberseliminated if desired.

In FIGS. 1 and 2 are shown schematically the cooperative relationshipbetween sealer blade 56 and cutter blade 60. Cutter blade 60 has step 62extending along its length, with cutting edge 64 extending along theouter end of the horizontal portion of step 62. Tapered surface 66recedes downwardly and inwardly from edge 64. The thickness of sealerblade 56 should generally be equivalent to the height of the verticalportion of step 62. Both cutter blade 60 and sealer blade 56 must belaterally alignable to permit sealer blade 56 to fit within step 62 toprovide cutting line 65 when the blades are in the closed positiondepicted in FIG. 2. The location of the step and the tapered surface maybe reversed however, with the step situated below the tapered surfaceand the sealer blade accordingly mounted laterally opposite it.

Blow assembly 68 is shown in FIG. 3, which comprises blowhead 70 andblowhead assembly arm 72. Channel 74 is provided in blow assembly 68 andis connected to a pressurized gas supply source, not shown.

The sequence of operations of this embodiment of the invention istypically as follows: As shown in FIG. 1, hot thermoplastic materialissuing from reservoir 15 of extrusion head I2 is extruded throughannular outlet orifice 14 to begin to form a generally tubular length ofthe material. Mold halves 18a and 18b are in the open position inregistry with extrusion head 12. Cutter and sealer blades 56 and 60 arelikewise in open position, after having previously cooperatively closedto sever the previous unit and seal the open end of the next succeedingparison, the sealed end shown at 78 in FIG. 1. During extrusion of theparison, and preferably after one-half to twothirds of the length of theparison necessary to form an article has been extruded, control valve 32is opened to permit introduction of low pressure, puff gas throughpassageway 28 in inner core 22 into the tubular length being formed, topartially expand the tubular length into bulblike shape 76. Afterformation of partially expanded bulblike shape 76, mold halves 18a and18b are closed around it as shownin FIG. 2, with tail 78, which wasformed when the previously extruded bulblike shape was cut and sealed,being pinched in the usual manner at the bottom between cooperatingedges of the mold halves. Simultaneous with the closing of the moldhalves or immediately thereafter, the cutter and sealer blades areclosed and extrusion head 12 is removed from alignment with mold 18 withblowhead assembly 68 then brought into alignment therewith. Closing ofthe cutter and sealer blades is accomplished when piston 36, piston rod38 and rod extension 46 of scissors like assembly 34, shown in FIG. 4,are moved to the right under the influence of a suitably suppliedconventional pressurized fluid so that rod extension 46 is in theposition shown in outline form in FIG. 4. As rod 38 moves to the right,members 40 and 42 pivot about toggle pin 44 at one end and about pivotpoints 48 and 52 at their other ends, with the latter ends movingoutwardly, while support members 50 and 54 pivotally connected tomembers 40 and 42 at 48 and 52, also pivot about bushings 64 and 66 as aresult of this movement of rod 38. The ends of support members 50 and 54at 58 and 62 thereby move inwardly to cooperatively move cutter blade 60and sealing blade 56 into closed position as shown in FIG. 2, and inphantom outline in FIG. 4, thereby simultaneously severing the partiallyexpanded bulblike shape and sealing the bottom end of the nextsucceeding one. After remaining in the closed position momentarily, thedirection of movement of the piston 36 is reversed by conventionalmanipulation of the pressurized fluid flows, and the blades return tothe position depicted in FIG. 4 as another extrusion cycle commences.

Further expansion or blow molding of the partially expanded bulblikeshape into the finished article is performed after the mold is removedor as it is being removed from alignment with extrusion head 12, bydirecting pressurized fluid through channel 74 of blowhead assembly 68as illustrated schematically in FIG. 3. After the article is formed, themold may be opened after which the formed article may be removed orblown from the apparatus in the usual manner, and the waste tail at thebottom and sprue at the top of the article trimmed off by conventionalmeans.

As can be appreciated from FIG. 2 the top of partially expanded bulblikeshape 76 is kept open during the severing operation due to the influenceof tapered surface 66 of cutter blade 60. Maintaining the top of theenclosed bulblike shape open permits escape of preinflation air andkeeps the end of the bulblike shape in a belled out position to permitthe end of the blowhead assembly to enter.

In FIGS. 5 and 6 is schematically depicted an alternate embodiment ofthe cutting and sealing apparatus of the present invention whichfeatures pan'son gripping provisions. Cutter blade 80 and sealer blade82 are constructed similarly to those previously described except thateach here has an upwardly and outwardly tapering sealing surfacedepicted respectively at 84 and 86.

Cutter blade 80 is provided with two identical gripping assemblies 85aand 85b, as shown in FIGS. 5 and 6, only one of which will here bedescribed in detail. Gripping assembly 851: comprises sleeve or channelmember 88 which is joined to cutter blade 80. Channel member 88 haschannel 90 therein, within which movable jaw 92 may move horizontallyback and forth. Stop member 94 is connected to channel member 88 byconventional means, for example by bolt 96. Biasing means are providedby compression spring 98 which is connected at one end to stop member 94and at the other end to movable jaw 92 and is under compression when thecutter and sealer blades are in open position so as to urge movable jaw92 away form stop member 94. Sealer blade 82 has fixed jaws 100a and100i: attached thereto by conventional means, for example, by bolt 102.Conventional means (now shown) must be provided for limiting the maximumoutward movement away from stop member 94 of jaw 92 in channel member88. For example, a slot may be bored in jaw 92 in which rides a pinrigidly connected to channel member 88. The pin and slot arrangementwould prevent spring 98 from urging jaw 92 completely out of channel 90when the blades are in open position. Cutter and sealer blades hi) and82, gripping assemblies 85a and 85b and fixed jaws ltltla and Ib aretoggle mounted and fluid operated in a manner identical with thatpreviously described and depicted in FIG. 4.

When the process is operated with the apparatus depicted in FIGS. and 6,after partially expanded bulblike shape 104 has been inflated, cutterblade 80 and sealer blade 82 cooperatively close to sever bulblike shape104 and seal the end of the subsequent blank as depicted in FIG. 5. Onclosing, movable jaw 92 abuts against fixed jaw 100a and in so doingsqueezes, flattens, and grips a portion of the bulblike shape as showntypically at 1106 in FIG. 6. The top 108 of bulblike shape I04 remainsopen, however, because of the influence of downwardly tapering cuttingsurface 87 of cutter blade 80. While the bulblike shape is gripped andsupported in two places between gripping assemblies 85a and 85b and jaws100a and With, and with top 108 open to the atmosphere, somepreinflation air escapes and the partially expanded bulblike shaperelaxes and flattens out somewhat, before the mold halves are closedabout it. After closing of the mold, the blowhead assembly isconventionally moved into alignment therewith and then relaxed,stretched bulblike shape further expanded to the final articleconfiguration. The mold halves are then opened and the article removed,and the tail at the bottom and sprue at the top of the article as wellas the flash material formed by the squeezing action of the jaws at theupper end of the partially expanded bulblike shape are trimmed off byconventional means. The upward and outward taper of sealing surfaces 84and 86 facilitate removal of the sealed end of the subsequent bulblikeshape from that being cut when extrusion head 12 is vertically lifted,for example, away from the area where the seal was formed.

In this embodiment, when cutter blade 80 and sealer blade 82 are inclosed position without squeezed plastic therebetween, movable jawstypically shown at 92 and fixed jaws 100a and limb are initially set bymeans of an eccentric bushing previously described and shown at 64 inFIG. 5., so that their opposing end faces are in touching contact. Thehorizontal movement of the movable jaws permitted by means of springs98, thereafter permits gripping different thicknesses of plastic betweenthe fixed and movable jaws without need for adjusting the travel ofblades 80 and 82 on each occasion.

Use of the gripping provision of FIGS. 5 and 6 also permit supportingthe bulblike shape while it is being transported to a waiting mold, orwhile the mold halves move in on it as it hangs below the extrusionhead. It should be understood that the movable gripping jaws depicted inthis form of the invention may, if desired, alternatively be mounted onthe sealer blade with the rigid jaws mounted on the cutter blade.Ordinarily it makes no difference on which blade the movable jaws aremounted.

FIGS. '7, 8 and 9 illustrate still another modification of the techniquefor cutting and sealing a preinflated parison as herebefore described.In this embodiment cutting and sealing are performed by separate means,rather than by the same apparatus as depicted in FIGS. 1 and 2.Extrusion tip 113 of cylindrical inner core 110 of extrusion head 112has a frustoconical tapered portion 114 near its lower end, having anouter surface I16. Cylindrical end portion 11118 of extrusion tip 113 isconnected to tapered portion 114 at the lowermost extremity of taperedportion 114, and cooperates with shoulder 120 of extrusion ring I2I todefine annular extrusion outlet orifice 122 in extrusion head 112, wheninner core 116 is in an upper extruding position as depicted in FIG. 8.Reservoir 1115 is provided within extrusion head llll2. Inner core I It)has channel III which may be connected to a pressurized gas source (notshown) as mentioned previously. In this embodiment, the cutter bladedepicted previously is eliminated and replaced by a second sealer bladeidentical in construction to that previously described. Therefore,primary and secondary sealer blades I241 and 126 are provided withactivating means identical to that portrayed in FIG. 4.

In the operation of this alternate embodiment, the parison is expandedinto partially expanded bulblike shape IN by low pressure gas enteringthrough channel III as previously mentioned. While mold halves llfia and1812 are in open position surrounding bulblike shape I28, sealer bladesI24. and I26 are in spaced apart, open relationship and inner core M6 isin its upper extruding position, which position is depicted in FIG. b.As previously stated, preinflation commences when about one-half totwo-thirds of the length of parison necessary for formation of thearticle has been extruded. After partially expanded bulblike shape 12%has been formed, the flow of pressurized gas is interrupted by closing asuitable valve in the pressurized gas supply line to channel llllll (notshown but similar to 32 in FIG. ll) and inner core III) is moved axiallydownward so that outside surface 1116 of frustoconical tapered portionI14 momentarily compresses the extruding parison against shoulder 1120of extrusion ring 12R as shown in FIG. 7 so as to score and thin out thewall of the preinflated parison at this upper end point. Inner core 1116is thereupon moved axially upward to its previous extruding position asdepicted in FIG. 3. During this momentary compression of the upper end,there is a corresponding momentary interruption in the flow of hotthermoplastic in the flow channel of reservoir llllS. Simultaneous withor incrementally in time after the scoring of the end of partiallyexpanded bulblike shape I23, mold halves Ida and Iflb are caused toclose around the bulblike shape 12%, and extrusion head 1112 is liftedaxially upward and away from the mold 18, while plastic continues toissue from the extrusion outlet orifice in a generally tubular form.With this movement of the extrusion head and mold, the scored end of thepreinfiated bulblike shape is held by mold halves lllia and I812, andsufficiently stretched by the lifting head at the point where it isscored, so that is is torn or pulled apart from the end of thesubsequent blank as depicted in FIG. 8. As extrusion head I12 begins tomove axially upward, cooperating sealer blades I2 and 126 close as shownin FIG. 9 to seal the bottom of the continuously extruding tube fromwhich the next bulblike shape will be formed, and mold It is moved outof vertical alignment with extrusion head 1112 while another mold movesinto vertical alignment therewith, the outline of which is partiallyshown as 1311 in FIG. 9. When the bottom end is sealed, the preinflationgas shutoff valve is opened at the proper time during extrusion of thenext parison, to commence another cycle and extrusion head 1112 islowered between the halves of the subsequent mold (1131) while the nextbulblike shape is being formed.

After bulblilte shape 126 has been enclosed within the cooperating moldhalves with sealed bottom portion lllItI gripped at the bottom of themold between cooperating projections, or simultaneous with the closing,a conventional blowhead assembly is moved into alignment with the moldand the bulblike shape further expanded into the final articleconfiguration as described previously and typically illustrated in FIG.3.

As an alternate to the sealing of the parison end on the upward lift ofthe extrusion head in the embodiment of FIGS. 7-9, sealing may beaccomplished on the downward stroke prior to preinflation, but with thisprocedure the hot thermoplastic has a tendency to build up on the sealerblades.

Conventional apparatus, for example, pressurized air or hydraulicallyoperated piston means or cam drive means cooperating with an upwardlythrusting spring (not shown) may be employed to axially move inner coreI III. Similar conventional piston means may be utilized to open andclose the mold halves.

The above description and particularly the drawings are set forth forpurposes of illustration only and are in no way to be taken in a limitedsense.

As previously mentioned, this invention is directed toward an apparatusfor forming hollow plastic articles having neclc and body portions byextruding moldable plastic material from a supply source downwardlythrough an outlet orifice to form a generally tubular length of thematerial, clamping the tubular length below the outlet orifice to form aseal across the tubular length, injecting gas into the portion of thelength above the seal to partially expand said portion, enclosing thepartially expanded shape within a partible mold having adjacent neck andbody forming cavities, and further expanding the partially expandedshape to form the hollow article.

It is essential with the method and apparatus of the present inventionthat the parison be extruded in a downward direction whereby it may bepartially expanded while suspended below the extrusion nozzle under theinfluence of its own weight, and without the need for separate endsupport.

It will be understood that the means for supplying a timed flow of gasthrough the passageway in the mandrel is merely illustrative and that awide variety of alternatives may be employed to properly time andcoordinate the gas thus supplied with the several operations of theplastic blowing and extruding apparatus.

It will be appreciated that although the present invention employsmovement of the extrusion nozzle and blowhead assembly for alignment ofthese elements with the mold, the present invention includes theconverse movement within its scope, i.e., movement of the mold to alignit with the extrusion nozzle and blowhead assembly.

The center and sealer blades and their supports mounted on apneumatically operated toggle joint may be designed to close and open ona single stroke of the piston by providing a piston having a stroketwice the length of that previously described. In a process notrequiring preinflation wherein the parison end need not be sealed, thesealer blade may be replaced with a cooperating cutter blade. Thoughpneumatic operation is preferred, other types of moving or activatingmechanisms may be employed to operate the cutter and sealer blades.

Utilization of gripping jaws in conjunction with the cutter and sealerblades is particularly advantageous in the present invention since itpermits escape of some of the preinflation gas through the open top endof the partially expanded bulblike shape prior to enclosing it withinthe mold, thereby relaxing the bulblike shape somewhat. In doing so,however, the bulblike shape is not returned to a tubular form butremains in a thinned-out partially expanded state. Discharge of some ofthe preinflation gas from the bulblike shape prior to blowing decreasesthe possibility of formation of chill marks in the finished article.These are rough areas formed on the outside surface of the preinflatedparison when the preinflated parison touches the cooled walls of themold cavity on closing the mold. The plastic in these areas sets up soas to prevent further expansion during final blowing. Though it is notessential that the preinflation gas be partially vented prior to finalblowing, it is preferable that some of the gas be discharged.

Though the extrusion head may be stationarily mounted, it is preferredin the present invention that it be movably mounted as, for example,mounting for vertical movement as disclosed in US. Pat. No. 2,349,186.With this mounting method, after the preinflated parison is enclosedwithin the mold, the extrusion head is caused to bob upward a shortdistance while the parison and/or bulblike shape for the next articlecontinues to extrude out the orifice. A revolvable rotary turret tablecontaining a plurality of molds may be provided to index the loaded moldto one side and position an adjacent open empty mold into the positionoccupied by the previous one. The extrusion head is then caused to bobdown as the subsequent bulblike shape is being finally formed so as toposition it within the subsequent empty mold. This extrusion iscontinuous and is maintained at a rate approximately equal to thevelocity of the extrusion head as it bobs up and.

down. Though extrusion head lift is the preferred method, the systemcould also operate by utilizing the parison jaw gripping arrangementpreviously described to transport a preinflated parison either axiallyor horizontally to a movable mold from a stationary extrusion head at arate faster than the parison is being extruded.

Any plastic material capable of being blown may be utilized in thepresent invention. Typical materials are therrnoplastics such as low orhigh-density polyethylene, polypropylene, polymers of vinyl chloride orpolystyrene. As the density and toughness of the material increases, theamount of stretch achieveable increases. Unusually good results areobtained therefore with high density polyethylene which is such atypical and preferred material. Polyvinyl chloride is also of similarconsistency.

The resiliency, temperature and thickness of the plastic being extrudedwill determine the pressure of the preinflation gas required in thepresent invention. For most materials this pressure should be maintainedbetween about one-eighth to about 5 p.s.i. above atmospheric pressure atthe end of the inner core or mandrel of the extrusion head, and thetemperature of the gas between about 20 F. to about 150 F. Attemperatures below about 20 F., cold spots may occur in the innerparison surface with the result that preinflation of the parison may benonuniform. In the case of high-density polyethylene the pressure shouldbe between the limits of about one-fourth to about 3 p.s.i. aboveatmospheric pressure, and the gas temperature between about 50 F. toabout F. for unexpanded parison wall thicknesses between about 1/32 in.to about /4 in. and parison temperatures between about 380 F. to about460 F. At pressures less than one-eighth p.s.i. no appreciable expansionis realized. At pressures greater than about 5 p.s.i. expansion isexcessive and results in the undesirable, unexpandible chill or roughspots in the finished article previously mentioned. Also at such highpressures excessive flash is formed along the parting line of the moldhalves and bursting may even occur. Preinflation pressure determines theamount of radial expansion of the parison to be attained and may bevaried with the material being extruded and the extrusion temperature tocontrol the size of the bulblike shape so that it just touches or isslightly smaller in maximum width than the minimum projection within themold, thereby eliminating or minimizing chill marks.

It should be understood that with the axially movable mandrel embodimentof the present invention, the parison may be either severed completely,or scored so that the parison wall thickness is reduced such that aminimum pull by either a moving extrusion head or mold tears thebulblike shape from the end of the next succeeding parison. As thetapered lower portion of the mandrel wears with use due to its severingor scoring action, it may be replaced if designed to be removablyconnected to the bottom of the mandrel. Use of this embodiment separatesthe cutting and scaling functions of the blades thereby decreasingmechanical wear and optimizing the action of each.

With the process of the present invention, it should be noted thatsubstantially no axial stretching of the parison occurs during thepreinflation step but rather a generally radial expansion takes place.The time during which the preinflation air is on during extrusion alsodetermines the degree of radial expansion. ln the present invention thismay vary between 10 and 100 percent of the time to extrude the length ofparison required to form one article.

Furthermore, the complete article including the neck is molded in asingle step from the preinflated parison. Extrusion preferably iscontinuous rather than intermittent. Recirculation of the extrudingmaterial during mold changes is thereby eliminated.

The principal advantage of the method and apparatus of the presentinvention is the production of economical lightweight noncylindrical orirregularly shaped bottles having extremely uniform body walldistribution, while utilizing the same quantity of plastic material asin forming a cylindrical body. Distribution is improved since expansionis more uniform by use of a preinflated parison, that is, the distancebetween the wall of the mold cavity land the outside surface of thebulblike shape prior to final expansion is more constant.

With the preinflation or puff blow step of the present inven tion, theparison is expanded to a larger diameter than that which it has onissuing from the extrusion nozzle, and in so doing is thinned outuniformly. A smaller tubing may thus be extruded to provide the sameweight of plastic in the finished article. The extrusion ring and tipmay be reduced in size in blowing a large diameter article rather thanincreased as is necessary without use of the preinflation step.Utilization of a reduced orifice reduces the extruder discharge headpressure necessary to force the plastic through the orifice.Furthermore, a single extrusion ring and tip may be used in formingvarious different sized containers merely by varying the time thepreinflation gas is kept on and the pressure thereof.

Use of a reduced diameter parison also minimizes flash formation in thetail pinch area due to its undersized character.

The surface characteristics of the extruded parison prior topreinflation may be varied according to the method and apparatusdisclosed in copending application Ser. No. 391,920, filed Aug. 25,1964, assigned to Monsanto Company.

The scissors assembly of the present invention comprising the cutter andsealer blades or the dual sealer blades may be independently mountedbetween the extrusion head and mold(s) or may be connected eitherpermanently or removably to the extrusion head itself.

The apparatus of the present invention is applicable in forming anyarticle having neck and body portions, and is especially applicable tononcylindrical irregularly shaped bodies where it is necessary to blowone side further than the other e.g., those with oval, rectangular oroblong cross sections. it is particularly adaptable in forminghandleware bottles and most especially for handleware bottles havingnoncylindrical elongated cross sections.

Various other modifications and alterations will be readily suggested topersons skilled in the art. It is intended, therefore, that theforegoing be considered as exemplary only, and that the scope of theinvention be ascertained from the following claims.

What is claimed is:

ill

ll. Apparatus for forming hollow plastic articles having neclt and bodyportions comprising:

a. means for extruding moldable plastic material downwardly through anoutlet orifice to form a generally tubular length of the material, saidextruding means including an extrusion head having a verticallyextending cavity therein, said head having an inwardly directed shoulderat its lower end defining an outlet opening therein, an axially movablemandrel within said cavity having a passage therein for pressurized gasand an inwardly tapering lower end portion in axial alignment with saidshoulder adapted to move axially, momentarily downwardly substantiallyagainst said shoulder to at least partially sever the tubular lengthfrom the remainder of the plastic in the extrusion head;

b. a clamping assembly for clamping the tubular length below the outletorifice to form a sealed portion of the length having a closed bottomend;

c. first means for injecting gas into the sealed portion of the lengththrough the passage in the head to expand said sealed portion;

d. a partible mold adapted to close separately from the clampingassembly and having a cavity conforming to the shape of the article forenclosing the expanded sealed portion; and

e. second means distinct from said extruding means for injecting gas tofurther expand the sealed portion against the walls of the mold cavityto form the article.

2. The apparatus of claim 1 wherein the clamping assembly comprises apair of horizontally aligned sealer blades between said head and saidpartible mold, each having a generally rectangular cross section.

1. Apparatus for forming hollow plastic articles having neck and bodyportions comprising: a. means for extruding moldable plastic materialdownwardly through an outlet orifice to form a generally tubular lengthof the material, said extruding means including an extrusion head havinga vertically extending cavity therein, said head having an inwardlydirected shoulder at its lower end defining an outlet opening therein,an axially movable mandrel within said cavity having a passage thereinfor pressurized gas and an inwardly tapering lower end portion in axialalignment with said shoulder adapted to move axially, momentarilydownwardly substantially against said shoulder to at least partiallysever the tubular length from the remainder of the plastic in theextrusion head; b. a clamping assembly for clamping the tubular lengthbelow the outlet orifice to form a sealed portion of the length having aclosed bottom end; c. first means for injecting gas into the sealedportion of the length through the passage in the head to expand saidsealed portion; d. a partible mold adapted to close separately from theclamping assembly and having a cavity conforming to the shape of thearticle for enclosing the expanded sealed portion; and e. second meansdistinct from said extruding means for injecting gas to further expandthe sealed portion against the walls of the mold cavity to form thearticle.
 2. The apparatus of claim 1 wherein the clamping assemblycomprises a pair of horizontally aligned sealer blades between said headand said partible mold, each having a generally rectangular crosssection.